1. Field of the Invention
This invention relates to a non-contact IC card capable of transmitting and receiving data through electromagnetic waves, a terminal for use with the non-contact IC card, and a non-contact IC card system having the non-contact IC card and the terminal and, more particularly, to a non-contact IC card system in which an IC card can receive and transmit data reliably once the IC is started up.
2. Description of the Related Art
FIG. 20 is a block diagram schematically showing the construction of a conventional non-contact IC card 100, such as the one disclosed in Japanese Patent Laid-Open Publication No. 58-154080. Various memories, i.e., a ROM 2, a RAM 3 and an EEPROM 4, are connected through a bus 13 to a CPU 1 for controlling the operation of the non-contact IC card 100 (hereinafter referred to simply as "IC card"). The ROM 2 is a non-volatile memory for storing a program executed by the CPU 1, the RAM 3 is a volatile memory for storing processing results or the like, and the EEPROM 4 is a rewritable non-volatile memory for storing data to be specially preserved, for example, attribute information of the card. An input/output control circuit 5 for controlling the operation of receiving data from a terminal and outputting data to the terminal is also connected to the bus 13. A receiving coil antenna 6 and a transmitting coil antenna 7 are connected to the input/output control circuit 5. The receiving coil antenna 6 is connected through a receiving amplifier 8 and a demodulation circuit 9, while the transmitting coil antenna 7 is connected through a modulation circuit 10, a transmitting amplifier 11 and a drive circuit 12. A battery 14 for supplying electric power to electric circuit sections of the IC card 100, a clock generation circuit 15 and other components are incorporated in the IC card 100. The drive circuit 12 has a power supply terminal 12a through which electric power is supplied from the battery 14, a transistor 12b switched on and off by a signal from the transmitting amplifier 11 to drive the transmitting coil antenna 7, and resistors 12c and 12d for stabilizing the signal from the amplifier 11.
The operation of the IC card when a person who possesses the IC card passes, for example, through a gate controlled by a terminal (both not shown) will be described below. Signals in the form of electromagnetic waves are exchanged between the IC card 100 an the terminal. Since one antenna is used on each of the receiving and transmitting sides, data is serially exchanged between the IC card and the terminal.
When a startup signal transmitted from the terminal at all times is received by the receiving coil antenna 6 of the IC card, it is amplified by the receiving amplifier 8 with a predetermined amplification factor and is sent to the input/output control circuit 5 through the demodulation circuit 9. The clock generation circuit 15 in the IC card generates internal clock pulses thereby to start up the CPU 1. The CPU 1 started up receives a data signal which is then sent from the terminal in the same manner as in the case of the startup signal, deciphers the data signal, and rewrites data in the memories according to the result of deciphering or reads out data previously stored in the memories to make predetermined interpretation and determination on the basis of the data read out. The result of interpretation and determination is sent as a data signal to the transmitting amplifier 11 through the bus 13, the input/output control circuit 5 and the modulation circuit 10 to be amplified with a predetermined amplification factor. The amplified signal is supplied to the drive circuit 12 to be transmitted through the transmitting coil antenna 7 by being converted into electromagnetic waves.
The signal representing the result of interpretation and determination is deciphered in the terminal and the deciphered data is collated with data previously set. If it is determined that the deciphered data is correct, the gate opened and closed under the control of the terminal is opened by a permission signal from the terminal, and the permission to pass through the gate is expressed by a normal display or a normal sound.
Conventional non-contact IC cards are generally arranged as described above. In general, a non-contact IC card has the shape of a portable member and a size generally equal to that of ordinary magnetic cards, and has internal coil antennas formed as a spiral copper foil pattern by etching or the like. Generally, dispersions of the inductance L and the resistance R of coil antennas formed in this manner are very large and dispersions of the characteristics of chip capacitors (not shown) and other circuit elements are also considerable. Similarly, there are also dispersions of the characteristics of coil antennas and other components on the terminal side. Thus, the conventional IC cards and terminals have respective latent receiving sensitivity dispersions due to manufacturing errors. Therefore, in a case where an IC card and a terminal are at a distance from each other close to the limit of the communicable distance range, which distance is small enough to start up the IC card, there is a possibility of failure to receive data during data signal communication after the startup of the IC card, resulting in a communication error and failure to use the essential functions of the IC card.